EP1296640B1 - Use as thickeners in cosmetics of neutralized copolymers comprising weak acid units and strong acid units - Google Patents

Abstract

This invention relates to a cosmetic, dermatologic, pharmaceutical, or veterinary composition comprising at least one thickening and/or emulsifying polymer for an aqueous medium, such composition being obtained by polymerization: at least one unsaturated weak acid and at least one unsaturated strong acid such as AMPS, in the presence of a cross-linking or branching agent and optionally of a transfer agent and characterized by a water-soluble polymer fraction ranging from 5 to 50 percent by weight, preferably 8 to 35 percent. These acids are partially neutralized at the time of polymerization. The composition obtained surprisingly exhibits optimal cosmetic characteristics, in particular very high stability in the presence of electrolytes over a very wide pH range (1-13) as a result of selection of suitable polymerization conditions for the thickening and/or emulsifying polymer (neutralization rate, active matter concentration, strong/weak acid molar ratio).

Description

The present invention relates to the technical field of cosmetic, dermatological, pharmaceutical or veterinary and detergent compositions comprising at least one thickening and / or emulsifying polymer for aqueous medium.

• L'utilisation de polymères réticulés pour élever la viscosité de produits cosmétiques, pharmaceutiques ou techniques ( FR 2,416,723 )
• L'utilisation d'une dispersion de polymère comme épaississant de pâte d'impression pour textile ( EP 0,161,038 )
• Les compositions comprenant un polymère épaississant à base de monomères non ioniques tels que l'acrylamide, anioniques tels que l'acide acrylique ou cationiques, gonflant à l'eau. Les polymères sont obtenus sous forme d'émulsion inverse. Sont citées entre autres des applications comme les cosmétiques et surtout les impressions textiles ou sur moquette ( GB 2,077,750 )
• Les polymères épaississants obtenus sous forme d'émulsion inverse à base d'acides forts ( US 4,172,066 )
• Le brevet EP 0 503 853 qui concerne un épaississant à base d'AMPS et d'acrylamide.
• L'utilisation d'un monomère possédant un acide fort spécifiquement pour épaissir des milieux acides (application pétrole) ( GB 2,110,744 )
• Le procédé de préparation d'une composition sous forme de latex inverse d'un polyélectrolyte (homopolymère) anionique, branché ou réticulé, à base d'un monomère possédant une fonction acide fort ( WO 99/42521 ).

It is known in the prior art:

• The use of cross-linked polymers to increase the viscosity of cosmetic, pharmaceutical or technical products ( FR 2,416,723 )
• The use of a polymer dispersion as a thickener for a textile printing paste ( EP 0,161,038 )
• Compositions comprising a thickening polymer based on nonionic monomers such as acrylamide, anionic such as acrylic acid or cationic, swelling with water. The polymers are obtained in the form of an inverse emulsion. Examples include applications such as cosmetics and especially textile or carpet printing ( GB 2,077,750 )
• Thickening polymers obtained in the form of an inverse emulsion based on strong acids ( US 4,172,066 )
• The patent EP 0 503 853 which relates to a thickener based on AMPS and acrylamide.
• The use of a monomer having a strong acid specifically for thickening acidic media (petroleum application) ( GB 2,110,744 )
• The process for preparing a composition in the form of an inverse latex of an anionic, branched or crosslinked polyelectrolyte (homopolymer), based on a monomer having a strong acid function ( WO 99/42521 ).

Branched or crosslinked polymers based on acrylamido methylpropanesulphonic acid and on acryliane acid are thickeners and / or emulsifiers of acidic cosmetic composition. ( WO 99/36445 ).

The patent is still known EP 0 186 361 .

An extremely important technical problem in the industry concerned is to provide the final composition with some interesting properties such as touch and stability of the viscosity in the presence of electrolytes. A strong demand exists, the solution of which has not been satisfactorily provided by the prior art.

The corresponding technical problem is therefore to find compositions having a thickening capacity with respect to aqueous compositions that can be used in cosmetics, dermatology, in the veterinary or pharmaceutical field, and similar areas of body care products, and in particular improving the feel and stability. .

More particularly, thickening compositions are sought both at acid pH and basic pH, and especially those effective at very acidic pH, in particular pH 1 - 3 approximately, which corresponds to a particular technical problem, which is not properly solved by the products of the prior art, despite significant demand from the industry.

It is meant throughout the present application by "thickening and / or emulsifying polymer", a copolymer obtained by polymerization in the form of inverse emulsion as described in the patent. EP 0,161,038 .

However, it remains to improve the stability of the composition in the presence of electrolytes. Indeed, the viscosity (and therefore the consistency) of the final product tends to fall sharply in contact with the electrolytes, for example the skin. This results in disadvantages of comfort of use and performance.

An even more delicate and extremely important technical problem in the industry under consideration is therefore to provide the final composition with some interesting properties such as electrolyte stability. A strong demand exists, the solution of which has not been satisfactorily provided by the prior art. Thus, when characteristics called "very cool touch" are described, they are in fact the direct result of poor behavior of the viscosity of the polymer in the presence of electrolytes.

The invention relates to a family of thickening and / or emulsifying polymers of the type described in the patent EP 0 161 038 above, which makes it possible to thicken cosmetic, dermatological, pharmaceutical or veterinary compositions, both at acid pH and at basic pH, while at the same time providing the composition with optimal and never obtained cosmetic characteristics such as the touch and the stability of the viscosity. presence of electrolytes. The use of this type of polymer can also be considered to thicken any type of aqueous media, such as detergency.

The present invention relates to the use of a particular selection of this family of copolymers as thickeners and / or emulsifiers (in whole or in part) of cosmetic, dermatological, pharmaceutical, human or veterinary, or detergent compositions.

The composition obtained has surprisingly optimal cosmetic characteristics with in particular a very high stability in the presence of electrolytes in a very wide range of pH (1-13) thanks to a suitable choice of the polymerization conditions of the thickening polymer and / or emulsifier (degree of neutralization, percentage of soluble polymers, molar ratio of strong acid / weak acid, concentration of active material) leading to the aforementioned fraction of soluble polymers.

• 5 à 95% molaire d'au moins un monomère possédant une fonction acide faible, et de
• 5 à 95% molaire d'au moins un monomère possédant une fonction acide fort et
• caractérisé en ce qu'il présente une fraction de polymères hydrosolubles comprise entre 5 et 50% en poids (par rapport au polymère total ), de préférence entre 8 et 35%, la méthode de détermination de la fraction hydrosoluble étant la suivante :
  • la méthode est basée sur la séparation des microgels de polymère réticulé d'avec une solution de polymère, par centrifugation, et la teneur en polymère est déterminée avant et après par titration de colloides, sur la base de la précipitation stoechiométrique de particules colloidales chargées par titration par un polymère de charge opposée, en utilisant un indicateur visuel,
  et en ce que, au momemt de la polymérisation, la neutralisation de la globalité des monomères possédant une fonction acide est partielle et comprise entre 5 et 95%.

The invention therefore relates to the use as thickener and / or emulsifier for aqueous media (in whole or in part) of cosmetic, dermatological, pharmaceutical, human or veterinary or detergent compositions, of at least one polymer obtained by polymerization. of:

• 5 to 95 mol% of at least one monomer having a weak acid function, and
• 5 to 95 mol% of at least one monomer having a strong acid function and
• characterized in that it has a water-soluble polymer fraction of between 5 and 50% by weight (relative to the total polymer), preferably between 8 and 35%, the method for determining the water-soluble fraction being as follows:
  • the method is based on the separation of the cross-linked polymer microgels from a polymer solution, by centrifugation, and the polymer content is determined before and after by titration of colloids, on the basis of the stoichiometric precipitation of colloidal particles loaded by titration by an oppositely charged polymer, using a visual indicator,
  and in that, at the time of the polymerization, the neutralization of the entirety of the monomers having an acid function is partial and between 5 and 95%.

While not wishing to be bound by any theory, the Applicant considers that this feature which is extremely important from an industrial and commercial standpoint lies in the high proportion of water-soluble polymers.

The closest commercial products that report "cool touch", and therefore poor skin electrolyte resistance, do not exceed 2-3% of water-soluble polymers. It therefore seems to exist a threshold of properties around 5% (see test according to the invention at 6%). (The tests according to the invention are averages of three tests, in order to reduce the margin of error to the maximum).

It should also be noted that the polymers of the present application do not comprise neutral monomers, which is probably an important factor in obtaining the abovementioned advantages.

According to a most preferred embodiment, the polymers are additionally obtained in the presence of a crosslinking or branching agent and optionally a transfer agent.

According to a preferred embodiment, the polymerization is carried out in water-in-oil inverse emulsion.

According to a preferred embodiment, the degree of crosslinking (or branching depending on the case) is 50 to 3000 ppm (considering methylenebisacrylamide or MBA) relative to the polymer or equivalent crosslinking with a crosslinking agent of different efficiency, according to parameters known to those skilled in the art.

Under the same conditions, the polymer that would be obtained in the absence of crosslinking agent would have an intrinsic viscosity (I.V.) of 3 to 25 dl / g.

According to another embodiment, the polymerization concentration is from 15 to 55% by weight.

According to yet another embodiment, the polymerization is carried out optionally in the presence of a transfer agent.

Those skilled in the art will appreciate from their own knowledge the degree of transfer agent and crosslinking agent or branching to use to obtain a branched or crosslinked polymer. Those skilled in the art also know the chemical definition of these two categories of polymers, many previous books and patents dealing with such polymers. We will simply indicate in the present application "crosslinked or branched" or "crosslinked" and similar terms, to recall the foregoing.

It is moreover essential that at the time of the polymerization the neutralization of the entirety of the monomers having an acid function is partial and between 5 and 95%. The polymerization pH varies depending on the degree of neutralization. It is thus possible according to the invention to work at a pH where the corrosion problems of industrial equipment are reduced very clearly, to the point that special equipment is not necessary. In particular, we will work at pH> 4 in polymerization, preferably 4.2-4.5, noting that below pH 4 (and although the pH difference in absolute value may seem very low), special anti-corrosion equipment is required. Thus the (non-limiting) possibility offered by the invention to work at polymerization pH of slightly more than 4 represents another interesting and surprising technical threshold.

By virtue of this appropriate choice of the polymerization conditions of the thickening and / or emulsifying polymer (neutralization rate, concentration of active ingredient, strong acid / weak acid molar ratio), the composition obtained surprisingly has optimal cosmetic characteristics such as the touch. and stability in a very wide range of pH (1-13), while maintaining a very strong and very effective thickening power, even at very acidic pH, especially at pH 1 - 3 approximately.

An optimization of the polymerization conditions will be accessible to those skilled in the art upon reading the present description and according to his personal knowledge, or with the aid of simple routine tests.

It is also possible to concentrate or isolate the polymer by any known technique.

• La précipitation dans un milieu non solvant tel que l'acétone, le méthanol et autres solvants polaires. Une simple filtration permet alors d'isoler la particule de polymère.
• La distillation azéotropique en présence d'agent agglomérant et de polymère stabilisant qui permet de conduire à des agglomérats que l'on isole facilement par filtration avant de procéder au séchage de la particule.
• Le « spray-drying » ou séchage par atomisation ou pulvérisation qui consiste à créer un nuage de fines gouttelettes d'émulsion dans un courant d'air chaud, pendant une durée contrôlée.

In particular, there are numerous processes for obtaining powder from soluble or water-swellable polymer emulsions which consist in isolating the active material from the other constituents of the emulsion. In a non-limiting way, it is possible to mention techniques such as:

• Precipitation in a non-solvent medium such as acetone, methanol and other polar solvents. A simple filtration then makes it possible to isolate the polymer particle.
• Azeotropic distillation in the presence of agglomerating agent and stabilizing polymer which leads to agglomerates which are easily isolated by filtration before drying the particle.
• "Spray drying" or spray drying which consists in creating a cloud of fine emulsion droplets in a stream of hot air for a controlled period of time.

• 10 à 80% molaire d'au moins un monomère possédant une fonction acide faible
• et de 20 à 90% molaire d'au moins un monomère possédant une fonction acide fort.

According to a preferred embodiment, the copolymer is obtained from:

• 10 to 80 mol% of at least one monomer having a weak acid function
• and 20 to 90 mol% of at least one monomer having a strong acid function.

According to a particular embodiment, the degree of neutralization (at the time of polymerization) of all the unsaturated acids is preferably from 10 to 80%.

Most preferably, a crosslinking agent or branching agent and optionally a transfer agent is incorporated.

According to another particular embodiment, the degree of crosslinking is preferably between 100 and 800 ppm (considering the MBA) relative to the polymer or equivalent crosslinking with a crosslinking agent of different effectiveness.

In the absence of crosslinking agent, the intrinsic viscosity I.V. of the polymer obtained is preferably 4 to 20 dl / g

The polymerization concentration is preferably from 25 to 45% of active material by weight.

The overall neutralization rate of the monomers having an acid function is between 20 and 90% at the polymerization

During the polymerization in the form of a water-in-oil emulsion, the continuous phase used may be an oil or a solvent of mineral origin and / or of synthesis and / or of plant origin. Preferably, a solvent or a non-mineral oil will be used.

• monomères présentant une fonction de type acide sulfonique, acide phosphonique, par exemple : l'acide 2-acrylamido-2-methylpropane sulfonique (AMPS).

The following is a non-limiting list of strong acid monomers:

• monomers having a function of sulfonic acid, phosphonic acid type, for example: 2-acrylamido-2-methylpropanesulphonic acid (AMPS).

Below is a nonlimiting list of monomers with weak acid function: acrylic acid, methacrylic acid, itaconic acid, crotonic acid, maleic acid, fumaric acid, etc. .

The following is a nonlimiting list of crosslinkers: methylenebisacrylamide (MBA), ethylene glycol di-acrylate, polyethylene glycol dimethacrylate, diacrylamide, cyanomethylacrylate, vinyloxyethylacrylate or methacrylate and formaldehyde, glyoxal, compounds of the type glycidyl ether such as ethylene glycol diglycidyl ether, or epoxy or any other means well known to those skilled in the art for crosslinking.

Below is a non-exhaustive list of transfer agents: isopropyl alcohol, sodium hypophosphite, mercaptoethanol, etc.

It will be understood that it will be within the abilities of those skilled in the art to select, under the conditions and ranges of implementation above, the optimum conditions such that the final polymer has a water-soluble polymer fraction of between 5 and 50% by weight relative to the total polymer (according to a method of assay of the type of that described p 8 of the patent EP 0 343 840 ), (AT). The skilled person will appreciate in particular from his own knowledge the degree of transfer agent and crosslinking or branching agent to be used to obtain a final polymer having a sufficient water-soluble polymer fraction, and the degree of neutralization to choose to obtain a polymerization pH slightly above 4 (if desired).

The skilled person will choose the best combination based on his own knowledge and the present description, as well as examples that follow.

Examples of polymers:

Each of the polymers described below was obtained by polymerization in the form of an inverse emulsion as described in the patent. EP 0,161,038 . To better compare them, the levels of crosslinking agent and limiting agent were kept constant.

It appears from the results obtained that the behavior (thickening power and electrolyte resistance capacity) is directly a function of the polymerization conditions and in particular the neutralization rate and the strong acid / weak acid molar ratio.

The choice of the polymer used is then a function of the characteristics required for the final composition. P1 P2 P3 P4 P5 P6 X % molar AMPS (strong acid) 60 60 60 40 50 90 57 % molar Ac. Acrylic (weak acid) 40 40 40 60 50 10 43 % Neutralization (total) 70 50 3 6 55 60 70 57 % Active ingredient 35 35 30 30 30 35 38 % Water Soluble Polymer 17 6 15 10 28 20 3 QC1 (viscosity measurement at pH = 3) 6000 16500 12000 3250 4500 12500 12000 QC2 (viscosity drop by addition of salts) 54 70 43 54 44 60 99.9

It would probably be technically possible to increase the proportion of water-soluble polymers above 28%, but without great interest, because it seems that the limit of the compromise is reached around 25 - 30 - 35%, depending on the details. application.

On the other hand, as already indicated, there is clearly a property threshold between the known products (at 2 - 3%) and the example of the invention at 6%.

It is also quite surprising that such a brutal threshold exists between 3 and 6%, which was neither predictable nor logical.

The fraction of water-soluble polymers may therefore preferably be between 6 and 35%, and even more preferably between 8 and 30% -35%.

• Préparation d'une solution A à 1% en poids de matière active dans de l'eau déionisée puis ajustement du pH entre 2,9 et 3,1 en utilisant de l'acide chlorhydrique 1 N
• Mesure de la viscosité n°1 à l'aide d'un viscosimètre Brookfield de type RVT : les valeurs obtenues sont en centipoises

QC1: viscosity measurement at pH = 3

• Preparation of a solution A at 1% by weight of active ingredient in deionized water and then adjusting the pH between 2.9 and 3.1 using 1N hydrochloric acid
• Measurement of the viscosity No. 1 using a RVT type Brookfield viscometer: the values obtained are in centipoises

• On ajoute à la solution A une solution saline (à 70 g/l de NaCl) afin d'obtenir une concentration finale en sel de 1 % massique par rapport à la matière active (polymère)
• Mesure de la viscosité n°2 à l'aide d'un viscosimètre Brookfield de type RVT : les valeurs obtenues sont en centipoises
• La chute de viscosité est calculée ainsi : $$\mathrm{Chute\; de\; viscosité}\left(\%\right)=100\times \left(\left(\mathrm{viscosité}1-\mathrm{viscosité}2\right)/\mathrm{viscosité}1\right)$$
  

QC2: drop in viscosity by addition of salts

• A solution of saline (at 70 g / l of NaCl) is added to solution A in order to obtain a final salt concentration of 1% by mass relative to the active ingredient (polymer).
• Measurement of viscosity No. 2 using a Brookfield viscometer of the RVT type: the values obtained are in centipoises
• The drop in viscosity is calculated as follows: $$\mathrm{Drop\; of\; viscosity}\left(\%\right)=100\times \left(\left(\mathrm{viscosity}1-\mathrm{viscosity}2\right)/\mathrm{viscosity}1\right)$$
  

It can be noted that, surprisingly, the products of Examples P1 to P6 exhibit good stability of their viscosity in the presence of electrolytes, which is not the case for product X. The level of water-soluble polymer appears to play a primordial role. . Given this good resistance, the polymers of this invention retain a high viscosity even at extremely acidic pH, unlike products known on the market.

Examples of compositions:

• Composant A : copolymère réticulé de type P1 comprenant 60% d'AMPS et 40% d'acide acrylique utilisé sous forme d'émulsion distillée contenant 62,6% de polymère
• Composant B : même polymère que le polymère A utilisé sous forme de poudre obtenue par « spray-drying »

In the context of the examples of compositions, the two polymers used correspond to the polymer previously described under the name P1. This polymer was chosen because it shows a good compromise between the QC1 and QC2 values. However, it is quite possible to use also one or other of the polymers presented, this selection depending only on the final characteristics required for the composition.

• Component A: P1 type crosslinked copolymer comprising 60% of AMPS and 40% of acrylic acid used in the form of a distilled emulsion containing 62.6% of polymer
• Component B: same polymer as polymer A used in powder form obtained by "spray-drying"

The names of the ingredients used in the compositions are those referenced under the INCl nomenclature ("International Nomenclature of Cosmetic Ingredients").

Example 1: base for a gel / cream, pH 3.6:

% in weight Aqueous phase : glycerin 2% water (aqua) QSP 100 citric acid QS pH = 3.5 Component A 3% preservatives Q S perfume Q S citric acid QS Final pH = 3.6

Operating mode :

• 1 ^st step: preparation of the aqueous phase.
• ^2nd step: adjustment of the pH of the aqueous phase by addition of acid.
• 3 ^rd step: adding component A with stirring.
• ^Step 4: adding preservatives and perfume.
• ^Step 5: pH adjustment to 3.6

Final characteristics of the composition :

• pH = 3.6
• viscosity (RVT 6, 20 rpm) = 10250 cP = 10250 mPa.s
• appearance: gel / cream white, opaque and glossy
• touch: unctuous because this gel / cream breaks very gradually on the surface of the skin. Texture: light, non-greasy and non-sticky
• easy grip with the hand while the texture is relatively smooth

Example 2: silicone lotion, pH 6:

% in weight dimethicone 10% octyl palmitate 5% water (aqua) QSP 100 Component A 1,5% preservatives QS perfume QS

Operating mode :

Ingredients are incorporated in the order listed. Component A, the preservatives and the perfume are then added with stirring.

Final characteristics of the composition :

• pH = 5.8
• viscosity (RVT 6, 20 rpm) = 9500 cP = 9500 mPa.s
• appearance: shiny cream, easy to take by hand
• touch: unctuous and light, does not make "water" to the application. Velvety final touch

Example 3: capillary cream base, pH 5:

% in weight water (aqua) QSP 100 Olive oil (Olea Europaea) 2% Component B 1.25% preservatives Q S perfume Q S citric acid QS pH = 5

Operating mode :

Component B is poured into the water. The oil is then added with stirring. As soon as the preparation is homogeneous, the preservatives and the perfume are added. The pH is adjusted to 5.

Final characteristics of the composition :

• pH = 5
• viscosity (RVT 6, 20 rpm) = 11500 cP = 11500 mPa.s

EXAMPLE 4 Oil / Cleansing Emulsion Base, pH 4.7:

% in weight Aqueous phase : Disodium Laureth sulfosuccinate 4% (m.a.) glycerin 3% water (aqua) QSP 100 (m.a. = active ingredients) Oily phase: caprylic / capric triglyceride 6% Sweet almond oil (Prunus Amigdalus Dulcis) 2% Component A 4% conservatives Q S Perfume Q S

Operating mode :

The aqueous phase is prepared. The oily phase is then incorporated. Component A is then added with stirring, followed by the preservatives and the perfume.

Final characteristics of the composition :

• pH = 4.7
• viscosity (RVT 6, 20 rpm) = 4000 cP = 4000 mPa.s
• aspect: white milk
• touch: little foam, easy to rinse, easy to spread while maintaining a consistent non-greasy and non-sticky texture.

Example 5: oil / water emulsion base, pH 4.2:

% in weight Oily phase "Shea Butter" (Butyrospermum Parkii) 2% (Shea Butter) Octyl stearate 8% Mineral oil (Paraffinum Liquidum) 4% water (aqua) QSP 100 Component A 2% preservatives QS perfume Q S citric acid QS pH 4.2

Operating mode :

Preparation the oily phase at 50 ° C. Water is added and the temperature is maintained at 50 ° C. Component A is added with stirring.

The mixture is then brought back to room temperature in order to add the preservatives and the perfume. The pH is then adjusted.

Final characteristics of the composition :

• pH = 4.2
• viscosity (RVT 6, 20 rpm) = 2750 cP = 2750 mPa.s
• aspect: opaque white fluid
• touch: light and consistent, allows the massage without forming particles uncomfortable for the consumer

Example 6: base for a gel / cream, pH 10:

% in weight water (aqua) QSP 100 Component A 3% NaOH QS pH = 10 preservatives Q S perfume Q S

Operating mode :

Component A is poured into the water. The pH is adjusted to 10. The preservatives and the perfume are then added with stirring.

Final characteristics of the composition :

• pH = 10
• viscosity (RVT 6, 20 rpm) = 12000 cP = 12000 mPa.s
• appearance: gel / cream white, opaque and glossy
• touch: unctuous. The gel is easy to spread.

The above examples show the diversity of compositions that can be targeted for the use of this type of polymer both for their thickening and / or emulsifying properties.

The improvements obtained are numerous:

The thickening and / or emulsifying polymers as defined can be incorporated at any temperature. They also offer great flexibility as to the incorporation step.

They are effective thickening and emulsifying polymers and therefore excellent stabilizers for compositions containing silicones, vegetable oils, ingredients in salt form or containing salts, or having a pH of less than 6.

Each of the final compositions tested has optimal cosmetic characteristics such as feel and stability.

The touches resulting from the various formulations are unctuous: at the time of application, the texture of the composition of the invention "breaks" less rapidly, which makes it possible to avoid a touch that is too "aqueous" (which looks like water), unattractive to the consumer, especially in terms of efficiency and comfort of the composition.

This property also makes it possible to prevent the composition applied to the surface of the skin, hair, nails or hair from flowing too quickly. It is then easier to control the application and the spread of the composition on the surface to be treated.

It should be noted that for each of the possible formulas, the choice of packaging is vast: pump bottle, tube, spray or "spray", pot,

In addition, the use of a polymer in the form of a powder is an additional choice. It makes it possible to benefit from the properties of the polymer as described above while avoiding the presence of the oily phase (solvent of the polymer) in the final composition. This possibility offers additional diversity to meet new technical and / or marketing requirements.

Claims (18)

1. Use as a (total or partial) thickener and / or emulsifier for aqueous media in cosmetic and dermatological compositions, pharmaceutical compositions for human or veterinary use, or detergents, of at least one polymer obtained through polymerisation of:

   - 5 to 95 mole % of at least one monomer having a weak acid function, and of

   - 5 to 95 mole % of at least one monomer having a strong acid function and

   - wherein the polymer contains a fraction of hydrosoluble polymers of between 5 and 50% by weight (of the total polymer), preferably between 6 and 35%, preferably 8 and 30-35%, the method for determining the hydrosoluble fraction being the following:

   - the method is based on the separation of the cross-linked polymer microgels with a polymer solution, by centrifuging, and the polymer content is determined before and after by colloid titration, on the basis of the stoichiometric precipitation of charged colloidal particles through titration of a polymer of the opposite charge, using a visual indicator, and wherein, at the moment of polymerisation, the neutralisation of the totality of the monomers having an acid function is partial and between 5 and 95%.
2. Use of a polymer according to claim 1, wherein the polymerisation is carried out in an inverse water-in-oil emulsion.
3. Use of a polymer according to claims 1 and 2, wherein more polymers are obtained in the presence of a cross-linking or branching agent, or possibly a transfer agent.
4. Use of a polymer according to any of claims 1 to 3, wherein the rate of cross-linking or branching is between 50 and 3000 ppm (considering the methylene-bis-acrylamide or MBA) in the polymer, or an equivalent level of cross-linking with a cross-linking agent with a different effectiveness.
5. Use of a polymer according to any of claims 1 to 4, wherein the polymerisation concentration is between 15 and 55% by weight.
6. Use of a polymer according to any of claims 1 to 5, wherein the polymerisation is possibly controlled by the presence of a transfer agent.
7. Use of a polymer according to any of claims 1 to 6, wherein said polymer is obtained from:

   - 10 to 80 mole % of at least one monomer having a weak acid function and from

   - 20 to 90 mole % of at least one monomer having a strong acid function

   - and possibly more in the presence of a cross-linking or branching agent and possibly a transfer agent.
8. Use of a polymer according to any of claims 1 to 7, wherein the rate of neutralisation (at the moment of polymerisation) of all the unsaturated acids of said polymer is preferably between 10 and 80%.
9. Use of a polymer according to any of claims 1 to 8, wherein the cross-linking or branching rate of said polymer is preferably between 100 and 800 ppm (taking into account the MBA) in relation to the polymer or an equivalent level of cross-linking with a cross-linking agent with a different efficiency.
10. Use of a polymer according to any of claims 1 to 9, wherein under the same conditions the polymer obtained without a cross-linking agent has an intrinsic viscosity (IV) of 3 to 25 dl/g.
11. Use according to any of claims 1 to 10, wherein the polymerisation concentration is preferably 25 to 45% by weight of the active material.
12. Use according to any of claims 1 to 9, wherein the overall neutralisation rate of monomers having an acid function is between 20 and 90% during polymerisation.
13. Use according to any of claims 1 to 12, wherein during polymerisation in the form of water-in-oil emulsion, the continuous phase used may be an oil or solvent of mineral and/or synthetic and/or vegetal origin, preferably a non-mineral solvent or oil.
14. Use according to any of claims 1 to 13, wherein said polymer comprises as a monomer one of the following strong acid monomers:

    - monomers presenting a sulfonic acid function or a phosphonic acid function, for example: 2-acrylamido-2-methylpropane sulfonic acid (AMPS).
15. Use according to any of claims 1 to 14, wherein said polymer comprises as a monomer one of the following weak acid monomers:

    - acrylic acid, methacrylic acid, itaconic acid, crotonic acid, maleic acid, fumaric acid.
16. Use according to any of claims 1 to 15, wherein said polymer has been cross-linked (or branched) by one of the following cross-linking agents: methylene-bis-acrylamide (MBA), ethylene glycol diacrylate, polyethylene glycol dimethacrylate, diacrylamide, cyano methyl acrylate, vinyloxy ethyl acrylate or methacrylate and formaldehyde, glyoxal, glycidyl ether type components such as ethylene glycol diglycidyl ether, or epoxies.
17. Use according to any of claims 1 to 16, wherein said polymer comprises one of the following transfer agents: isopropylic alcohol, sodium hypophosphite, mercaptoethanol.
18. Use according to any of claims 1 to 17, wherein said polymer is formed by means of inverse emulsion polymerisation using: P1 P2 P3 P4 P5 P6 % mole AMPS (strong acid) 60 60 60 40 50 90 % mole acrylic acid (weak acid) 40 40 40 60 50 10 % (Total) Neutralisation 70 50 36 55 60 70 % Active Material 35 35 30 30 30 35 % Hydrosoluble Polymer 17 6 15 10 28 20 QC1 (viscosity measurement at pH=3) 6000 16500 12000 3250 4500 12500 QC2 (fall in viscosity by adding salts) 54 70 43 54 44 60